FIELD OF THE INVENTION
This invention relates to a method in the continuous dehydration of tertiary butyl alcohol using catalyst wherein water formed in the dehydration reaction is continuously removed from the reaction zone.
The dehydration of tertiary butyl alcohol, TBA, to form isobutylene is well known. The reaction is a relatively simple one to promote, high temperature alone will convert tertiary butyl alcohol to isobutylene, though it is usually preferred to use a catalyst.
U.S. Pat. No. 3,510,538 (U.S. Class 260-682), the teachings of which are incorporated by reference, discloses a continuous process for dehydration of tertiary butyl alcohol which uses as an acid-acting catalyst cation exchange resins, preferably the sulfonic acid type cation exchange resins.
This reference also discloses the use of benzene in the dehydration zone. The benzene forms an azeotrope with the water produced during dehydration of TBA. The benzene-water azeotrope and produced isobutylene are removed as a vapor from the dehydration zone and the vapors cooled to permit condensation of benzene and water but not isobutylene. A water phase is withdrawn from the process, benzene is recycled to the dehydration zone, and isobutylene product is recovered as a vapor.
The process described in that patent is reasonably satisfactory, but is not very efficient in handling TBA feed streams which already contain a significant amount of water.
TBA is usually produced by hydrating isobutylene in the presence of sulfuric acid catalyst, or other acid-acting catalyst such as sulfonic acid type cation exchange resins. It is inherent in many of these processes that the TBA produced contains a substantial amount of water. Water and TBA form an azeotrope, so the only way to remove water from TBA by distillation is to add an additional azeotrope forming agent, such as benzene, to separate water and TBA. Significant energy must be used to vaporize the water, and the material forming an azeotrope with the water.
In the days of inexpensive energy, fractionation costs were relatively low, and petrochemical manufacturers could tolerate the increased utilities demand caused by watery TBA feed to a TBA dehydrator. There was also no practical way known, until now, to remove the water which was present in the TBA feed to the dehydrator, so removal of water was simply accepted as part of the process.